The objective of this research will be to determine factors which may alter the concentration of estradiol-17 Beta, estrone, progesterone, cortisol, and their metabolites in cow's milk. Initial research will be directed toward validating for milk our existing methods used to quantify these steroids in blood serum. These studies will involve measuring extraction efficiencies, recoveries of radioactivity and mass of the steroids. We also plan to determine the relative distribution of the steroids amongst the lipid, water and cellular phases of milk. After validation of the assays is complete, milk collected from lactating cattle will be assayed for steroid hormone concentrations during the estrous cycle, pregnancy, lactation stage, and during various phases of inflammation. The effects of milk processing and storage conditions on the steroids will also be determined. Another aspect will be to inject radioactive hormones into the mammary artery, and recover the hormone and its metabolites at subsequent intervals.